College of Science and Engineeringhttps://hdl.handle.net/1969.6/132019-01-21T23:05:15Z2019-01-21T23:05:15ZCharacterization of an induced morphological defense in the Eastern Oyster Crassostrea virginicaScherer, Avery E.https://hdl.handle.net/1969.6/11702017-06-05T20:45:40Z2017-05-01T00:00:00ZCharacterization of an induced morphological defense in the Eastern Oyster Crassostrea virginica
Scherer, Avery E.
To reduce their risk of consumption, many prey species use plastic defenses that are employed in situations where predators pose high risk of injury or death. By modifying prey traits, predators often exert strong influence on community structure and function. These nonconsumptive effects can be stronger than effects from prey consumption, but have only become the focus of study in recent decades. Further, they are often more complicated than consumptive effects because they can be influenced by characteristics of the predator, the prey, the response type, and the environment. In order to fully understand the effects of predator species on prey organisms, prey responses must be fully characterized and understood in an ecological context.
Eastern oysters Crassostrea virginica were selected as a model organism to investigate the costs, benefits, and mechanisms of predator-induced changes in prey traits. Oysters are an ecologically and economically valuable species, known to increase their shell weight and strength in response to crab predators. In this study, oyster responses were investigated by 1) fully characterizing the mechanism and cost of oyster responses to predation risk, and determining the effect of 2) risk cue type (predator versus prey), 3) an ecological prey characteristic (size), 4) an ecological predator characteristic (diet), and 5) an environmental characteristic (food availability) on defense induction.
In response to risk, oysters increased calcium carbonate production to rapidly reach a size refuge from predators. This led to an inverse relationship between shell thickness and shell density. Although not significant, there was a trend for reduced gonad investment in oysters which had thick, low density shells. As this study provides a conservative estimate of defense costs, this suggests oysters may experience reductions in reproduction under conditions of high predation risk which may be exacerbated under conditions of ocean acidification.
Oysters responded to all tested cues indicative of risk, but responses were less intense when oysters were exposed to cues from injured prey organisms or to predators which were food deprived or fed aged oyster tissue. In addition, oyster responses were inversely related to oyster size. Oysters responded to predators regardless of resource availability, despite reduced shell metrics in response to limited food under control conditions.
There is a diverse array of factors which influence oyster defenses and which may be altered by anthropogenic disturbance. If oyster defenses reduce investment in reproduction, this could have important long-term consequences for oyster populations and oyster reef communities. Therefore, understanding factors which influence prey responses allows us to understand conditions which promote or attenuate nonconsumptive predator effects. And understanding the costs of these effects for organisms allows us to predict the effect of disturbances on community structure and function.
A dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in MARINE BIOLOGY from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
2017-05-01T00:00:00ZWill small diversions of freshwater inflow affect water quality?Olson, Cheyanne Mariehttps://hdl.handle.net/1969.6/11672017-06-05T20:34:09Z2017-05-01T00:00:00ZWill small diversions of freshwater inflow affect water quality?
Olson, Cheyanne Marie
Freshwater inflow is a vital component of an estuary, as several ecological relationships exist between the level of inflow and aspects of estuary function. For future management, it is necessary to know how diversions of freshwater inflow may affect both water quality and ecosystem function within estuaries. The purpose of this study was to examine the effects of variation in freshwater inflow to make inference about water quality variables and estuary function during low inflow periods. This study focused on three bays: Carancahua Bay, San Antonio Bay (including Guadalupe Bay), and Tres Palacios Bay. Data was collected monthly via water quality sampling, and with continuous and discrete multiparameter sondes. Acoustic doppler current profilers (ADCPs) collected current speed and direction daily. Hourly precipitation and wind data was collected from the National Climatic Data Center (NCDC). Daily discharge was collected from two USGS flow gages. Freshwater inflow is responsible for driving nutrient concentrations and salinity ranges, as demonstrated by a principal component analysis. Based on results of this study, San Antonio Bay requires a large amount of freshwater inflow change (above 10,000 ac-ft/mo) to yield changes in water quality response, because it typically receives large volumes of inflow. Conversely, Carancahua Bay and Tres-Palacios Bay both require smaller volumes of freshwater inflow (less than 10,000 ac-ft/mo) to have large (i.e., 30% change) effects on water quality response because these bays receive lesser amounts of inflow. Freshwater inflow also alters net ecosystem metabolism (NEM) of an estuary. Freshwater inflow and salinity both had a significant but weak correlation to NEM when lagged, due to a time lag experienced between drivers and estuary response. The flow-to-water quality concept created in this study provides a generic framework that can be applied by managers and policy-makers to analyze how specific amounts of flow diverted from, or added to, specific bays may alter water quality conditions.
A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in ENVIRONMENTAL SCIENCE from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
2017-05-01T00:00:00ZUnderstanding species diversity of the amphidromous Indopacific goby genus Stiphodon (Gobiidae: sicydiinae)Lor, Yerhttps://hdl.handle.net/1969.6/11662017-06-05T20:34:09Z2016-08-01T00:00:00ZUnderstanding species diversity of the amphidromous Indopacific goby genus Stiphodon (Gobiidae: sicydiinae)
Lor, Yer
Gobies constitute a great majority of fishes seen in oceanic island fish communities. Of particular interest in these communities are the amphidromous gobies of the subfamily Sicydiinae. Adult gobies spawn upstream in freshwaters from which newly hatched larvae are washed downstream to the sea. These larvae spend anywhere between 91-265 days at sea before returning to freshwater streams. This marine pelagic larval phase is believed to be the main mechanism behind the spatial and temporal dispersal of these species. However, very little life history information is known about these gobies. Males of the genus Stiphodon are brightly colored, but females are drab in coloration and pattern. Male coloration is the primary characteristic used to distinguish between these species, however, subtle differences in male coloration, overlapping distributions, as well as a lack of diagnostic morphological characteristics makes it difficult to distinguish species. Historically, most studies have been on identifying and describing species of Stiphodon by using morphological and pigmentary characteristics. More recently, molecular systematics and phylogenetic methods have been used to infer species delineations. This study is the most comprehensive phylogenetic analysis of this genus using three nuclear genes to determine species diversity and relationships among species. All nuclear phylogenetic trees support monophyly of the genus and recognize the presence of two clades, one more diverse than the other.
A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER of SCIENCE in MARINE BIOLOGY from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
2016-08-01T00:00:00ZRespiratory physiology of belugas (Delphinapterus leucas)Epple, Alexandra L.https://hdl.handle.net/1969.6/11652017-06-05T20:34:09Z2016-08-01T00:00:00ZRespiratory physiology of belugas (Delphinapterus leucas)
Epple, Alexandra L.
Though cetaceans withstand long periods of apnea and exhibit short respiratory exchange periods, many of the fundamental physiological mechanisms underlying cetacean respiration are unknown. This study examined respiratory durations, volumes and flow rates in nine belugas (Delphinapterus leucas) housed in managed care facilities using custom designed pulmonary function equipment.
Large differences were observed among the animals, including vastly different tidal volumes (7.5 20.7 L) and vital capacities (29.8 93.0 L). Measurements of vital capacity may have been affected by behavioral compliance with requested maximal effort cues, but may also have allowed for measurement of larger ranges past those obtainable without training.
Animals exhibited high flow rates with a maximal recorded flow rate of 371 L∙sec–1; slower and less variable inspiratory flows indicate a potential physiological flow limitation not exhibited during expiration.
Tidal volumes were much larger than those predicted based on respiratory scaling equations and were 43 % of the vital capacity. Though previous research suggests that cetaceans may be capable of exchanging 80-90 % of their total lung capacity, these animals were not regularly doing so.
These findings expand upon data previously collected in other species by establishing novel data on respiratory variables in belugas. Development of a healthy baseline could allow for non-invasive investigation into beluga respiratory health.
A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER of SCIENCE in MARINE BIOLOGY from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
2016-08-01T00:00:00Z